Applying polyester onto metal substrate

ABSTRACT

The present invention is a laminating process which is directed toward economical production methods for scalable amounts of production which develop properties suitable for a broad based product line. In particular, the product is capable of important key components of commercial properties such as adhesion, scratch resistance, chemical inertness, and bending without failure.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation in part of U.S. Pat. No. 7,942,991filed on Feb. 18, 2009 which is a continuation in part of U.S. Pat. No.7,678,213 filed on Sep. 11, 2006 which claims the benefit of U.S.Provisional Application No. 60/716,053 filed on Sep. 13, 2005. Allreferenced applications are incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO SEQUENCE LISTING, A TABLE, OR COMPUTER PROGRAM LISTING

Not applicable.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

This application is directed to laminating films in either the molten orsolid state onto metal substrates. In particular, applying polyesterfilms onto preheated metal substrates through a chemical bond in acommercially viable process whereby multiple desirable commercialproperties are simultaneously developed.

(2) Description of Related Art

Others have described laboratory processing steps related to puttingfilms onto metal surfaces. For example, U.S. Pat. No. 5,330,605describes preheating a metal strip and then laminating a biaxiallyoriented copolyester resin film. However, a post treating step has beenfound to be necessary for permanent commercial adhesion in manyimportant markets, and the post treating step substantially destroys thecrystallinity of an oriented polyester film. Since crystallinityprovides important commercial pencil hardness and toughness properties,the hardness and toughness of the film will be lowered in actual use.U.S. Pat. No. 5,149,389 and U.S. Pat. No. 5,093,208 describes a thermallaminating process where a metal strip is preheated, laminated, postheated, and quenched in water. The process targets the creation ofnon-crystalline polyester coating that is generally useful for canmaking. Unfortunately, the lack of crystallinity is a distinctdisadvantage in creating desirable commercial characteristics such aspencil hardness, chemical resistance, and toughness in bending (i.e.coating continuity).

U.S. Pat. No. 5,318,648 describes a thermal laminating process where thecooling process is specifically performed to avoid creatingcrystallinity in the laminate film. This has similar problems withpencil hardness and toughness properties just described.

U.S. Pat. No. 3,679,513 describes a thermal laminating process for apolyethylene. The process does not describe pretreating the metalsurface by raising the surface energy nor does it describe methods ofcreating crystallinity in the finished laminate film to develop pencilhardness or bending toughness. Polyethylene is not known to developdesirable commercial properties and the low melting point ofpolyethylene is undesirable for many markets when compared to otherpolymers.

U.S. Pat. No. 5,679,200 describes a thermal laminating process forapplying a film to a metal strip where the laminating rolls provide aspecific force. The patent is directed toward a specific laminating nipforce related to avoiding the pickup of film onto the nip rolls. Theprocess does not describe pretreating the metal surface by raising thesurface energy nor does it describe methods of creating crystallinity inthe finished laminate film.

U.S. Pat. No. 5,695,579 describes a thermal laminating process where thepolymer coated metal is rapidly and immediately quenched after posttreating to ensure that the coating is amorphous. The described processis designed to avoid creating crystallinity in the finished laminatefilm. The process does not describe pretreating the metal surface byraising the surface energy nor does it describe methods of creatingcrystallinity in the finished laminate film.

Others have worked on important commercial—technical issues such as theeliminating entrapped air between the film and metal substrate. Forexample, U.S. Pat. No. 6,200,409 describes an improved laminatingprocess which works on eliminating air bubbles by heating the laminatingnip rolls and preheating the film prior to laminating. Similarly, U.S.Pat. No. 6,164,358 describes efforts at reducing air entrapment by usinga support roll with a projected film angle. In the later disclosure, acommercially acceptable amount is defined as an 8% area covered byentrapped air. Others, such as U.S. Pat. No. 5,679,200, have attemptedto handle trapped air through increased nip forces.

Important commercial markets are open to lamination provided thatacceptable adhesion, pencil hardness, bending toughness, and corrosionprotection can be simultaneously achieved. These markets are currentlyserved by the pre-painted coil coated industry. Typical products includethe following:

Building and Construction Products such as:

-   -   a. Roofing and Siding    -   b. Exterior Accessories    -   c. Structural and Mechanical    -   d. Interior Components    -   e. Manufactured Housing    -   f. Garage Doors    -   g. Doors and Windows

Transportation Products such as:

-   -   a. Passenger Cars, Vans, and Light Trucks    -   b. Trucks and Semi-Trailers    -   c. Buses    -   d. Travel Trailers and Recreational Vehicles

Business and Consumer Products such as:

-   -   a. Large and Small Appliances    -   b. Electronics    -   c. Water Heaters and Water Softeners    -   d. Heating and Cooling Equipment    -   e. Home and Office Furniture    -   f. Window Equipment    -   g. Toys and Sporting Goods    -   h. Fixtures and Shelving    -   i. Lighting

Containers and Packaging Products such as:

-   -   a. Cans, Ends, Tabs, Crowns, & Closures    -   b. Barrels, Drums, and Pails    -   c. Strapping and Seals    -   d. Draw and Ironed can bodies

Other/Miscellaneous Products such as:

-   -   a. Machinery and Industrial Equipment    -   b. Electrical Equipment    -   c. Signs and Displays

It is important to note that the referenced patents have not resulted ina commercially viable high production thermal laminating line in the US.The difficulties in simultaneously scaling up production, creating aneconomically viable process, and developing suitable commercialproperties have been strong barriers to the actual implementation of alaminating process. The previous efforts by others have been lacking inimportant technical aspects of cooperation between the processing steps,economic viability, and suitable commercial properties.

Current high production laminating methods on thicker metal substrates,i.e. 0.005″ and above, are primarily directed at utilizing press onadhesives which are applied by a roller onto the metal substrate, andthe adhesive is dried in an oven prior to the laminating step. Thisprocess is commonly part of a commercial coil paint line. Theapplication of the film to the metal substrate is generally done closeto ambient temperatures. The adhesive is separately applied to the metalsubstrate and is usually not a part of the film, such as a multilayerfilm.

It is important that high production thermal laminating methods havelittle or no entrapped air between the metal substrate and the film.Entrapped air causes thinning of the coating at an unpredictable amount.In particular, when a formed part is bent and the bend occurs where anair bubble exists in the coating, an increased likelihood of failureresults. Air entrapment is a serious issue when the air bubble size issignificant relative to the coating thickness, and the frequency ishigh. It is also visually disturbing at an 8 percent level to acustomer, on a surface area basis, and raises unnecessary questionsabout process control.

Although laminating methods which utilize a press on adhesive layer arepresently employed in some areas of the marketplace, it is notconsidered a reliable or permanent bond for many markets. In particular,the market is resistive for architecture panels or outdoor exposedpanels due to prior failures.

It is important that the coating has the necessary pencil hardness, thatis, surface scratch resistance, and also suitable bending capability.Coating hardness must be balanced against brittleness. A hard coatinghas an increased likelihood of splitting on the bend of a formed part.If the coating splits, the metal is exposed and there is likelihood of acorrosive failure at that spot.

In summary, it has been difficult to develop the necessary simultaneousproperties for a commercial thermoplastic coating on a thick metalsubstrate at an economical cost. The coating needs the simultaneouscapability of: developing suitable bonding to the metal substrate,economical production, having suitable pencil hardness, eliminating airentrapment, and having the ability to withstand a tight metal bendwithout splitting.

BRIEF SUMMARY OF THE INVENTION

The present invention is a laminating process which is directed towardeconomical production methods at scalable amounts of production whichdevelop properties suitable for a broad based product line. Inparticular, the product is capable of important key components ofcommercial properties such as adhesion, scratch resistance, chemicalinertness, eliminating air entrapment, and bending without failure.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1 shows a preferred embodiment commercial line of the presentinvention.

FIG. 2 shows a preferred embodiment of a laminating station.

FIG. 3 shows another embodiment of a laminating station.

FIG. 4 shows an embodiment where the excess film is trimmed afterlamination.

FIG. 5 shows a general embodiment of the present invention.

FIG. 6 shows an embodiment where the film roll(s) will be positioned totrack the position of the metal strip.

FIG. 7 shows another preferred embodiment commercial line of the presentinvention.

FIG. 8 shows another preferred embodiment of a commercial line of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is a laminating process that simultaneouslycreates desirable commercial products in a crystalline polyester filmdue to its unique position as an affordable engineered polymer. Inparticular, essential commercial characteristics of scratch resistance,bending toughness, and permanent adhesion are developed which are highlycompetitive to paint. Polyester is generally more affordable than otherengineered polymers in the marketplace, and is chemically similar tomany paints which are short chain polyesters admixed with cured epoxies.

When considering current pricing trends in thermoplastics, the betterpriced plastics tend to be polyethylene (high density, low density,linear low density), polystyrene, polypropylene, ABS, acetalhomopolymer, and polyester (both PET and PBT). This is in reference tothe types of polymer grades that are reasonably available in volumepricing that are extrudable at a commercial speed for a thermoplasticcoating of around 1.0 to 1.5 mil thick. However, it has been founddifficult to find satisfactory coating performance among many of thelower priced polymers, in particular, the polyolefins. Surface scratchresistance, in particular, has been elusive. The higher priced polymers,such as Acrylic, Fluoropolymers, Liquid Crystal Polymers,Polyamide/imide, Polyarylate, Polyetherimide, Polyetherketone,Polyphenylene Sulfide, Polysulfone, Cellulosics, Polycarbonate andPolyurethane are financially unappealing. Table 1 shows a roughaffordability ratio for the same coating thickness on a price per poundwhen considering the polymer specific gravity. Although Table 1 could beshown as various ranges depending upon the polymer grades chosen, it isa rough average for a simplified view.

TABLE 1 Polyethylene 1.0 Polypropylene 1.1 Polystryene 1.2 PVC 1.2 ABS1.3 Polyester 1.7 Acetal 1.8 Polycarbonate 2.3

FIG. 1 shows a simplified commercial laminating line for a flat rolledmetal substrate. A payoff reel 10 with an air brake pays off a metalsubstrate, passes under a deflector roll 11, and continues to acontrolled natural gas-air premix burner 12 where the surface energy ofthe strip surface is raised to a minimum dyne/cm level of 45. Thisminimum dyne/cm level has been found necessary to create an initial bondbetween the metal and film, and also to prevent air entrapment betweenthe film and metal surface. In a preferred embodiment, the dyne/cm levelis at least 55 for the best initial bond of film to the metal substrate.

The surface to be coated is preferably free of debris, oils, water, andother liquids for proper adhesion. The metal surface is preferablyconversion coated, pretreated, or coated with an organic primer, butthese kinds of treatments are not required for proper adhesion. Thesekinds of pretreatments significantly enhance the ability of the metal toprovide corrosion protection. The air brake provides back tensioncontrol for the line. In line surface cleaning of the metal substrate isdesirable if surface contaminates, particularly oils, are in place todisrupt the bond between the polymer and the metal surface. In linesurface cleaning could include dip tanks with suitable cleaningsolutions, rinse systems, and electrical grid systems.

The air premix burner 12 also provides preheating of the metal to atleast 200° F. The preheat prepares the metal surface to receive the filmwithout air entrapment, and also to establish an initial chemical bondwith the film. In one embodiment, the preheat is at least the meltingtemperature of the tie layer within the film, if one is used, or thesoftening point of the polyester film if a lower temperature tie layeris not used. It has been found that here has to be at least some bondestablished at the laminating nip that will carry over to the posttreating step. The post treating step will then establish the finalcommercial adhesive bond.

In some cases, the initial bond at the laminating nip, over a twentyfour hour period, will achieve a high strength bond such as may possiblybe used for stamping and roll forming operations without the need for apost treating step. However, this proved to be unreliable from acommercial quality control standpoint, and the post treating step isgenerally considered to be needed for a reliable, fully commercialoperation.

It is possible that the need for a post treating step may reliably beavoided by various primer coatings, along with a suitablepretreat/preheat step. However, this was not researched by thoroughexperimentation and is only theorized by examining material that waspartially processed on a laminating line or extrusion line without apost treating step. The final bond appears to be related to bettersurface cleanliness (i.e. high surface energy) along with filmcleanliness.

The extrusion coating line can be set up to closely match the width ofthe film to the metal substrate width. The molten film can be applied tothe metal substrate and then trimmed by a ‘hot wire’ type of trimmerclose to the nip point. Alternately, the film may be trimmed whensolidified by a cooling roll and then applied in the solid form at thelaminating Nip Rolls. Alternate, the film may also be applied with aflat paper ribbon adjacent to the metal substrate so as to provide adisposable coated medium for over width polymer. The coated flat paperribbon may then be trimmed away from the coated metal substrate.

If an extrusion coating process is used, it is possible to measure thecolor of the coating and vary the amount of color mix added to thehopper to match Hunter 1, a, b color scale values. A feedback loop maybe employed to make appropriate corrections on line. This way, thinnercoatings may compensate for opacity issues, such as when the metalsubstrate color becomes part of the final color of the finished product.

In an embodiment the air premix burner 12 is automatically regulatedbased on the line speed. This ensures that the line is capable ofcorrectly controlling the preheat temperature for various changes thatare needed, and to allow a higher production rate after initial settingsare established at a lower speed.

A laminating station 13 provides preselected films for laminating to oneor both sides of the metal substrate by a pair of nip rollers. The niprollers press the films onto the metal substrate by use of a compressedair cylinder, hydraulic cylinders, screws, mechanical springs, or othermechanical means to create a force. The rolls are heated, but not sohigh as to cause the films to melt or to have a preferential adherenceto the laminating rolls rather than to the metal substrate. If two filmsare applied, each side of the metal substrate may have a distinct filmor the same film. In the normal case, the temperature of the rolls willgenerally be set to match the preheat temperature of the metal strip,but this is not a strict requirement. Some variance below or above thestrip preheat temperature may be preferred, depending upon the type offilm being laminated. However, the continuous strip feeding into thelaminating nip will have a strong tendency to drive the laminating rollsto the strip preheat temperature, unless cooling or heating is provided.Cooling could be provided by backup rolls to the laminating rolls whichare water or air cooled.

Generally, a threshold nip pressure is required to establish an initialbonding without air entrapment, as well as the needed pressure to ensurethat the metal substrate is flat in the nip so that the film is allowedto bond to the metal. However, air entrapment was not found to becorrelated to nip pressure at the line speeds studied (i.e. below 100fpm).

The metal-polymer laminate then proceeds to the post treating inductionfurnace 14 where the strip is heated to at least the melting point ofthe lowest melting layer polymer in either film. That is, if a two layerfilm is used, a tie layer that melts at 200° F. and a polyester layerthat melts at 430° F., the metal-polymer laminate will be heated to atleast 200° F. In a preferred embodiment, the metal-polymer laminate isheated to a point where all of the polymers are melted to ensure acomplete bond of the polymers to each other and to the metal substrate.The exit temperature from the post treating step is carefully controlledby regulating the power to the heating induction coils and monitoringthe exit temperature with a suitable sensor; such as an infra-red sensor20. Induction furnaces that are capable of heating metal strips areknown in the art. A small amount of nuisance smoke is a likelyoccurrence from the polymer, and is readily removable by vent ductwork19 a with a suitable vent fan 19 b. Alternately and equally, the stripcan be heated by other means which include infra-red, gas flame heating,convection, conduction, electrical resistance, and a gas fired furnace.

In another embodiment, the post treating heating rate is automaticallyregulated based on the line speed, optionally utilizing a curve thatincludes any efficiency effects that vary with the line speed. Thisensures that the line is capable of correctly controlling the post treattemperature for various changes that are needed, and to allow a higherproduction rate after initial settings are established at a lower speed.For example, if an induction system is used, the power input isregulated based on line speed. If a gas fired system is used, the gasBTU input rate is varied with the line speed.

For the post treating operation, a direct flame impingement, or flameheating by close flame proximity has been found to be a viableembodiment of the present invention, but not without some trouble on theprocessing line. If the polymer is not carefully controlled to be insidethe edges of the metal strip, the direct flame on the overhangingpolymer is likely to cause melting or burning of the overhangingpolymer. This can cause operational problems such as smoking, polymerdripping, and minor flames which may cause unsafe or unclean operationalpractices. However, by controlling the polymer film position within thewidth of the metal strip, and properly applying it in the laminatingstep to have initial adherence across the strip width, then the posttreating by flame impingement will be satisfactory for at least somecommercial applications. Even heating was found to be obtainable by thismethod, as observed by cooling effects of solidifying polymer that wasrelatively even and symmetric across the strip width.

The polymer metal laminate then proceeds to the exit cooling section 15where cooling is allowed to take place either by natural convection orforced convection. In the present invention a crystalline polyester isused and the exit cooling section is designed to allow the crystallinestructure to develop. In the exit cooling section, the polymer willsolidify and cool down to the point where the crystalline structuredevelops and is well established. Air blowing devices 16, such as fromcompressed air nozzles, fans, and the like, can be employed to create adesigned cool down rate for the metal polymer laminate (forcedconvection). An exit deflector roll 17 is used just prior to the windingreel 18. The cool down rate can be matched to the polyester used inorder to enhance or contain the crystallinity to a satisfactory level toestablish desired commercial properties. Generally, a higher amount ofcrystallinity is needed in order to develop a higher pencil hardness. Itis the normal case to maximize crystallinity. However, for some markets,higher crystallinity may make the polymer brittle and may need to bebalanced against the forming requirements for a particular application.The exit deflector roll 17 can be optionally utilized as a contactcooling roll by adding water cooling. Other cooling rolls could be addedto create a designed cool down rate for the polymer.

Preheating the metal substrate prior the laminating above 350° F.provides suitable initial bonding from a process standpoint, but otherfactors begin to require consideration, such as economics and equipmentcapability. It is more expensive to operate laminating rolls in thehigher temperatures, i.e., above 350° F. Their life is lower and theirreplacement cost is higher. Also, preheating the metal substrate abovethe melting point of a polyester film can cause the surface of thelaminating rolls to heat up, and create a situation where the filmbegins to stick to the laminating rolls rather than the metal substrate.It is preferable to maintain the preheat temperature of the metalsubstrate below the melting point of the polyester film to avoid thiscomplication. However, this is not a strict requirement. The polyesterportion of the films tend to have melting points from 375 to 465° F.,depending upon the type of film, as well as additives and mixtures addedinto the polyester portion. One embodiment of the present invention isto maintain the preheating of the metal strip below the melting point ofthe outside layer of the film. Another embodiment is to provide heatingand cooling of the laminating rolls to allow any desired metal substratepreheat temperature above 200° F.

For many markets, a surface finishing pinch roll 09 with a designedsurface finish is used to imprint a desired surface finish into thepolymer surface while it is still in the melted state. The rolls arepreferably water cooled, but can be cooled by other means such as air.The designed surface finish can be used to control the surfacereflectivity, which in turn controls the surface gloss. This is adesirable outcome for some markets, in particular, where the glossrequirements are very low. Also, various desirable surface finishes canbe imprinted such as anti finger print, matte finishes, highlyreflective finishes, logos, or light embossed patterns. In general, thesurface finish roll cools the polymer below the melting point to ensurethe polymer does not stick to the surface finishing roll. Use of asurface finishing roll is an important embodiment of the presentinvention.

FIG. 2 shows a close up of a preferred embodiment of a laminatingstation. A metal substrate 21 has already been pretreated and had thesurface energy elevated as explained in FIG. 1. Film from an upper andlower film roll 22 a,b passes over an idler roller, 23, 27 and thenproceeds to a trimming station 24, 26 where one or both sides of thefilm is trimmed. This provides for matching the film width to the widthof the metal substrate. The trimmings 29 a,b from each side is vacuumedaway in a vacuum removal tube 28 a,b. This allows ordering films in lotsizes that are not the same as the metal substrate widths and providefor much better polymer inventory control. Every width in every possiblecolor does not have to be stored. Also, the width of the film isestablished just prior to the nip rather than after the laminating step.It is a preferred embodiment to side trim the film just prior to the nipas it is less troublesome and more reliable to do it there. The knivesmay be score cut, razor cut, or shear slitting.

The film trimming knives 24, 26 may be moved to match the position ofthe metal substrate on the line if there is any off tracking from theline centerline. A metal substrate edge sensor may be employed tomonitor any metal substrate off tracking, and reposition the knives toensure the film edges match the metal substrate edges. In this case,positioning sensors are added to the knives or a ball screw is employedwith a shaft encoder. Edge sensors include devices based on infraredlight, capacitance, visible light, LED, air, CCV, lasers, and others. Ina preferred embodiment, the substrate edge is sensed within 0.005″ andthe knives are positioned by a control system so that the film with ismatched within 0.010″ of the metal substrate. However, in commercialpractice, a film to metal mis-match tolerance of up to 0.125″ may beacceptable for some markets and is a minimum acceptable control.

In a commercial setting, it is preferable embodiment that the overallcontrol of the film width and position is maintained so that there isvery little film overhang or that the exposed metal does not exceedabout 1/32 of an inch on either edge. In another embodiment, bare metalon the edge is commercially acceptable up to ⅛ of an inch.

It is an important embodiment of the present invention to be able tocontrol the width of the film at the laminating process. The productionof films can be a very expensive undertaking, relative to otheroperating costs, and the ability to match the width of the film is animportant matter for best overall operating costs. Polymer films areexpensive to make when they are thin, as the operation of a cast filmline is generally a fixed amount per hour, and the width of the castfilm then becomes an important factor. It is preferable to maximize thewidth of the film through the film maker in order to improve costs,especially when exact steel widths are unknown or difficult to predict.It is especially important not to undersize the film width for aparticular order when running multiple widths on the cast film line witha single large width.

Though it is somewhat more troublesome, another embodiment of thepresent invention is to side trim 31 the film after the film has beenpressed on to the metal substrate as illustrated in FIG. 3. If thecontrol is carefully maintained, the knives will provide good stablecutting of the polymer only, with infrequent tracking up and onto themetal surface. It is preferable to reduce or avoid having the knivesroll onto the strip, as the reliability is better due to difficultieswith dulling or chipping of the knife edges.

FIG. 4 shows another preferred embodiment of the present invention wherethe film roll positions are dynamically matched to the strip position.The metal substrate 41 is laminated by films from two unwind film rolls42 a,b which are optionally side trimmed by trimmers 43 a,b. The edgeposition of the metal substrate is detected by an edge sensor 44 whichallows a mechanical control system to move one or both of the filmunwind film rolls 42 a,b to match the position of the film edge. If theoptional side trimmers 43 a,b are utilized, they are optionally moved tomatch the position of the metal substrate edge position. The movement ofthe trimming knives would depend upon whether there was sufficient widthof the film to trim. Generally, if the trimmers are utilized, it ispreferable for them to move with their respective unwind film roll tokeep the control simplified.

The edge sensor 44 utilizes an infra-red, other light type, capacitance,compressed air, or a mechanical style. The sensor may be analog,digital, or an on/off style such as a photoelectric sensor. An Infra-redsensor may be preferable for some polymers where good penetrationthrough the polymer is achievable and capacitance is preferable forothers. Routine experimentation is likely to be required to identify areliable sensor for a particular polymer, color, and polymer thickness.It is preferable that the sensor does not touch the metal or polymer,but this is not a requirement.

An embodiment of the present invention is to move both unwind film rollsby a single metal edge sensor. This provides a way to simplify thecontrol system and ensure that the film rolls are aligned to the metalsubstrate. A single frame that includes any film supporting rolls aswell as the film rolls can be moved to track any metal edge variance.The frame motion needed to follow the strip edge will only be a fractionof the actual line speed, that is the metal strip speed. The framemotion will only need to be about 2% or less of the line speed for goodcontrol. In a preferred embodiment, a control system will have avariable speed adjustment.

In a preferred embodiment, the bonding of the film to the metalsubstrate is by a chemical bond. The process design is set up aroundutilization of compounds that include maleic anhydride, acrylic acid,glycol, or an acrylate group. Commercial polymers that are useful in tielayers include, but are not limited to, Bynel (E.I. Du Pont De Nemours,Wilmington, Del.), Admer (Mitsui Chemicals America, Inc., Rye Brook,N.Y.), Plexar (Equistar Chemicals LP, Houston, Tex.), PETG (EastmanChemical Company, New York, N.Y.), and Amplify (Dow Chemical Company,Midland, Mich.). In particular, a maleic anhydride grafted polyethylenehas found to be very successful at developing the necessary bonding tometal at relatively low amounts of at least ¼ percent by weight in a tielayer. A typical tie layer that can be successfully co-extruded andprovide bonding between the metal and polyester is an anhydride-modifiedethylene acrylate. Ethylene based tie layers are preferred rather thanpolypropylene based tie layers which have been found to be poorlyadhering to polyesters.

In one embodiment of the present invention, a terpolymer is utilized asa tie layer. It has been found that a tie layer with both an anhydridefunctionality and an acrylate functionality will provide superiorbonding between metal and the polyester film.

PETG, or polyethylene terephthalate glycol, is a polyester based tielayer that offers higher pencil hardness and coating toughness incertain situations. The increased modulus of elasticity in comparison topolyethylene based terpolymers, such as Admer, for example, improvesperformance when the coating must undergo significant shear. It wasfound through practical experience that certain commercial stampingoperations performed decidedly better when a PETG tie layer was used.Failures, in some cases were completely eliminated during commercialtrial attempts when a polyethylene terpolymer failed. Also, a highersurface hardness is possible as the pencil hardness test includes asignificant shear component.

The post treating step ensures that the process provides a reliablecommercial bonding between the polyester film and the metal substrate.However, a number of laboratory measurements of suitable commercialbonding after the laminating step without post treating were observed.Adhesion values at or above 43 ounces per inch width as measured by across hatch adhesion test were observed. It is understood that thepreheat of the metal is sufficient to cause the tie layer to melt at thelaminating nip, if a tie layer is used, and cause the tie layer tobecome very chemically active for bonding purposes. The presentinvention is designed to ensure the reliability of the laminationprocess by including a post treating step in the coating process.However, based on laboratory measurements this is not a requirement inorder to create a coating that has adhesion at a commercial level.

For the purposes of this patent application,

-   -   i) a coating with an adhesion value of at least 43 ounces per        inch width is interpreted as a classification of 4 or 5 by ASTM        test method D3359 using a tape with an adhesion level of 43        ounces per inch. If there is an initial failure on a measurement        immediately after production on the processing line, a second        measurement is made 24 hours later after cooling down to ambient        temperature. A passing test on either adhesion test is        considered an adhesion value of at least 43 ounces per inch        width.    -   ii) a coating that has continuity of at least three metal        thickness bending radius without metal exposure means that the        metal polymer laminate does not split open so that metal        exposure can be seen either by the naked eye or by magnification        up to 100×. The radius bend is made by carefully and slowly        bending the metal substrate in a tight radius so that the        bending curve is substantially round. The radius is measured to        the inside metal surface of the bending radius at three        thickness and higher, that is, three thickness and bending        radius that are greater. Orange peel textures or localized        thinning of the polymer on the radius is normal and is not        considered a failure.    -   iii) a coating with a pencil hardness of a minimum of 2B means        2B or harder as measured by ASTM test method D3363.

The present invention has advantages in chemical inertness. Polyesters,even in thin films of 0.003″ and less, have significant corrosionresistance capabilities. Based on comparable salt spray results of U.S.Pat. No. 7,279,225, among others, it is understood that a polyesterinherently is very capable of withstanding corrosive commercialrequirements. Based on additional visual inspection of failures in asalt spray environment, where failures occur due to undercutting of thecoating (i.e. edge creep) and not due to porosity in the coating or acoating integrity failure, there is strong evidence of polyester'schemical resistance in a thin coating on a metal surface. Coatingcontinuity, therefore, on a bend is a highly important aspect formaintaining corrosion protection on a formed part.

FIG. 5 is a more generalized expression of the present invention. Eachstep will now be described.

Step 51: Uncoil strip—standard continuous (batch coil to coil or weldedwith inline strip storage) flat rolled strip.

Step 52: The surface energy of the metal strip surface to be coated isincreased by a controlled flame (i.e. air to gas ratio is controlled),corona, or plasma. The surface energy is raised to a minimum dyne/cmlevel of 45. The present invention has found that utilization of thiskind of pretreatment avoids difficulties reported by others with airentrapment. No air entrapment of any kind was observed at the laminatingspeeds seen, even when examined closely under a microscope.

Step 53: The metal strip is preheated to a temperature of 200 to 400° F.Acceptable methods that can be used include, but are not limited to,are: flame fired oven, infrared oven, direct flame impingement, nearlydirect flame impingement, convection oven, induction furnace, electricresistance heating, electric heating coils, gas fired furnace, andradiant heating. The present invention has found that utilization ofpreheating is necessary in order to avoid air entrapment between themetal surface and film. This step can be done simultaneously with step52 if a flame is used. In this case the dyne/cm level in step 52 isimmediately measured after the strip is cooled down, if verification isdesired.

Step 54: Laminate at least one side of the metal strip by use of a rollpair. One roll is optionally heated by a control loop. The preheatedstrip will heat the rolls anyway and the heated roll avoids startupissues. The width and position of the film must match the position ofthe metal strip. A second roll pair is utilized, if desired, forlaminating a second film in sequence to the first pair. If a second rollpair is utilized, an additional surface pretreatment is utilized toensure the surface energy of the second side to be laminated iselevated, as well as a heater if needed to obtain the proper preheattemperature at the second roll pair.

Step 55 a,b: Film—at least one is predominately polyester, that is, 50%by weight. Tie layers, colors, and various additives necessary for colordispersion may be added to the polyester which would lower thepercentage by weight. Also, admixed compounds that increase pencilhardness, provide surface lubrication, provide better processing,provide UV resistance, or create desired gloss are optionally added.

Step 56: The metal-polymer laminate is post heated, preferably byinduction heating furnace, above the melting point of the polyester.Equally, the post heating is done by flame fired oven, infrared oven,direct flame impingement, nearly direct flame impingement, convectionoven, induction furnace, electric resistance heating, electric heatingcoils, gas fired furnace, and radiant heating. An infrared sensor ispreferably installed to monitor the exit temperature to ensure propercontrol.

Step 57: After the post treating step, a surface finishing step isapplied to one or both surfaces of the polymer if needed for the marketsthe metal-polymer laminate is being sold to. A pinch roll is preferablyused to apply a surface finish while the polymer is still in the meltedstate. The surface finish transfer is a near duplicate copy of the rollfinish. The rolls are cooled to ensure the polymer does not adhere tothe rolls, but the metal-polymer laminate is maintained at a high enoughtemperature to allow the proper cool down rate and timing to develop thedesired crystalline structure. An alternate method is to utilize acontinuous belt, but this is somewhat less preferable as it is oftendifficult to create a good belt splice that is not visible. However, abelt is desirable for ease of switching between finishes.

Step 58: After the post treating step, a cool down rate is performedthat allows the polyester film to achieve desired crystallinity. Formost markets, the maximum amount of crystallinity will be desired.However, in some markets, the amount of crystallinity may be lower thanthe maximum in order to improve flexibility and forming.

Step 59: After the cool down step, the metal-polymer laminate isrecoiled at a temperature that will not cause problems with lap to lapshrinkage or slippage. Generally, temperatures less than 150° F. arepreferred to ensure there are no winding or storage problems.

An important and significant improvement of the present invention is toutilize equipment inline to improve the surface energy of the metalsubstrate prior to the laminating nip step. Such equipment is acontrolled flame (i.e. air to gas ratio is controlled), corona, orplasma. The surface energy is preferably raised to a minimum dyne/cmlevel of 45. The present invention has found that utilization of thiskind of pretreatment avoids difficulties reported by others with airentrapment. However, it must be used in combination with a preheating ofthe metal substrate to at least 200° F., and preferably 250° F. As aresult, no air entrapment of any kind was observed, even when examinedclosely under a microscope. It is believed that the combination ofpreheat and surface energy allows the film to instantly “wet out” andinitially adhere to the metal substrate. This pretreating method worksvery well for a metal surface, a conversion coated surface, an organiccoated surface, or even a surface that has a prior polymer coating.

Elimination of air entrapment between the film and metal substrateavoids the entrapped air from expanding in the post treat operation. Ifthe entrapped air bubble is significant in size, it can expand enough torupture through the film surface and allow metal exposure. Even if it isnot large enough to allow metal exposure, it may be large enough tocause coating thinning and then lower the corrosion protection at thespot of the entrapped air. The substantial elimination of entrapped airis an important result of the present invention.

As conceived in the present invention, air entrapment is not related tothe laminate nip roll pressure. In the examples following, only a verylight laminating force was used with light laminating springs which wereopened by rotating a hand knob. Higher line speeds are obtainable,therefore, without concern for problems observed by others.

It is preferable to have the cooling rate after the post heater designedto maximize the amount of crystallinity in the polyester. The exact cooldown rate will be polymer dependent. A semi-crystalline PBT, forexample, has been found to need only three to five seconds at atemperature range of 150 to 180° F. to develop its nearly fullycrystalline structure in the thin coatings of the present invention.That is, to develop the crystalline structure that it is capable ofdeveloping.

For the purpose of this invention, crystallinity is measured by aDifferential Scanning calorimeter (DSC) as is known in the art. Theamount of crystallinity is determined by the energy absorbed in thepolymer. To determine the percent of crystallization, a highlycrystalline form of the polyester is used for comparison as is known inthe art. In the case of a blend of PBT/PET, an average must be used.

One embodiment is to utilize a semi-crystalline polyester which rapidlyreaches its potential level of crystallization, within seconds aftersolidification in the post treating step of the coating process.Semi-crystalline polyester polymers, when used with a polyester tielayer are capable of achieving relatively high pencil hardness whenprocessed under the correct post treat temperature and cool down timing.

In some cases, it is desirable to have strip storage for longerprocessing runs of multiple coils rather than thread each individualcoil. The line may be stopped for each coil and the coil ends weldedtogether, as is common in coil processing lines, and a looping tower orlooping coil car employed. Such technology is known in the art. Also, astrip splicing or joining method may be employed with success, such as astitching/stamping method as by Behlen Manufacturing Company (Columbus,Nebr.). Any downstream rolls with a narrow or closed gap, such as pinchrolls, may be opened briefly to let the splice pass through to avoiddamage. Generally, splices do not affect or damage idler rolls in acoating operation provided proper care is taken. The pressure from thesplice onto the rotating rolls does not cut into rolls provided therolls are sufficiently tough. A disadvantage of adding looping towers tothe line is the additional capital cost and lengthening the amount ofthreaded strip in the line. For higher speed lines, 200 fpm and above,strip storage provides important production advantages.

It is desirable to have the ability to continuously run multiple rollsof film in sequence without stopping if metal strip storage is added tothe laminating line. In this case, the ability to switch over to filmsof different colors and widths is a distinct production advantage. Thisadds capital cost and operational complexity to the laminating line, butit also provides an overall lower operating cost and a better operation.It is not appealing to stop a line in the middle of a run for the sakeof starting a new film roll, as a customer will find yield losses andoff specification material objectionable in a finished coil. A new filmroll can be spliced to a previous running coil “on the fly” by methodsknown in the art, by taping ends of coils together without the use oflooping towers or coil cars. In fact, it is less desirable to addlooping towers to a processing line to make the processing of steelcoils continuous if the rolls of film are not continuous as well.

FIG. 6 shows an important embodiment of the present invention. An edgesensor 62 monitoring the metal strip 61 to be laminated is used toposition the upper and lower films going into the laminating roll pair69 a,b. The positioning of the films is done by positioning the upperfilm roll 65 by use of an upper T rail 63 a and slide channel 63 b wherethe entire film roll 65 is moved. Similarly, the lower film roll 66 ispositioned by use of a lower T rail 64 a and slide channel 64 b.Preferably, both the upper and lower film rolls are moved by use of oneedge sensor, however, two separate edge detecting sensors may be used.The upper and lower film rolls may be moved by one actuator, such as ahydraulic cylinder, air cylinder, or motor. The edge positioning circuitwill move slowly, at a top speed of less than 2 percent of the linespeed in order to prevent wrinkles from forming in the film and toensure stable tracking operation.

The mechanical film positioning system matches the film position(s) tothe strip position in the event the strip off tracks during the coatingoperation. A second optional sensor, not shown, can be used to positionthe side trimming knives 67, 68 on the second strip edge to ensure thefilm width matches the strip width. In this manner, the film can bepositioned to match the strip position if it is the same width, or thefilm is additionally trimmed on one side if it is wider than the strip.In a normal operation, the strip width is known and the film sidetrimming knives 67,68 may be appropriately positioned by use of a scaleor electronic position indicator. The positioning and sensing tolerancesof FIG. 6 are the same as already discussed in FIG. 2. FIG. 7 is anotherembodiment of the present invention that is very similar to FIG. 1 for aflat rolled metal substrate. A metal substrate 70 pays off an unwindreel and is surface pretreated and preheated by gas fired burners 71 toa controlled temperature. The metal substrate then goes through a firstlaminating step 72 where a film is pressed against the top major surfaceof the metal substrate by a top roll. The metal substrate then passesthrough two optional second steps of pretreating-reheating 73 by a gasfired burner and a second laminating step 74. The pretreating-reheatingmay be fired at a high enough rate to reheat the metal substrate if ithas cooled down too far prior to the second laminating step. The secondlaminating step presses a second film against the opposite major surfaceof the metal substrate by the lower roll. The second film may be thesame as the first film or it may be a different film. Depending upon themarket, some products may only require a simple “backer” type of filmwhere high performance is not required. In this case, a polyester filmmay not be required and a polyolefin may be utilized, such aspolypropylene or polyethylene. In other cases, the polyester may be onone side and a very high performance film may be utilized on the otherside such as a PVDF film or a polycarbonate.

A post treating operation by a direct impinging or direct fired gasfired flame 75 is utilized in combination with an exhaust system 80 tocapture any nuisance smoke. An infrared temperature sensor 76 monitorsthe temperature of the polymer-metal laminate as it exits the posttreating step. An optional surface finishing roll step 77 is utilized. Adesigned cool down section 78 provides the needed crystallinity in thefinal polymer-metal laminate. An air blow off system 79 may be utilizedif necessary to provide forced air cooling in the designed cool downsection 78. The air blow offs 79 are preferably movable and locatableanywhere in the cool down section 78.

A double roll 81 of film is shown for ease of splicing two rolls ontothe top side of the metal substrate. The two rolls of film arepreferably spliced together dynamically while the metal substrate ismoving so that there is no line stoppage when switching between films.An automatic system of splicing utilizing two sided tape is provided asis known in the art. In this manner, colors, widths, and film types canbe readily changed when orders change or when one roll of film runs out.On the fly film splicing improves line economics as already discussed.Both top and bottom film splicing can be done, even though only the toproll of film is illustrated.

The present invention is generally conceived as a one or two sidedcoating process. It is preferably performed in a single pass for bestline and operational efficiency. However, one side at a time could becoated under some circumstances by choice, if equipment were notfunctional, or if multiple layers of film were to be placed on top ofeach other. Under such circumstances, the present invention could beadapted to the situation by uncoiling the metal substrate, pretreatingthe appropriate side(s), preheating, laminating, optionally posttreating, cooling, and winding up on a winding reel. Then the work inprogress coil would then be uncoiled a second time, and coated with filmaccording to the teachings of the present invention through a processingline a second time on one or both sides. Also, multiple films could belaminated in sequence on the same side by use of multiple pretreating,preheating, and laminating steps prior to post heating by adapting theteachings of the present invention.

As another embodiment of the present invention, multiple film widths canbe applied simultaneously to the metal substrate with a gap separatingthem. This is an important embodiment for some markets where parts willbe cut out and bare metal areas will be needed for welding. Inparticular, a three piece can body with a side welded seam maypre-coated on a wide metal tinplate by coating multiple film widths thatare separated by a small gap, such as a 1/16 and up to ¾″ wide. Thefilms could be split from a single film which is slit on line andseparated by gapping methods, or several films could be mounted andgapped.

In FIG. 8 a metal strip 80 is unwound from a coil, travels around twodeflector rolls, and passes through a pair of pretreatment burners 81which also simultaneously preheat the metal strip. The prepared metalstrip then travels to a pair of nip rollers 83 where a two molten films88 a, 88 b from extruder slot dies 82 a,b, or alternately coat hangerdies, are pressed against the metal strip. A pair of paper ribbons 801on top of the strip feed into the nip rollers 83 to catch any overhangmolten film so that it does not stick onto the nip rollers. The coatedpaper is subsequently trimmed by knives 802.

The metal polymer laminate then travels to a pair of post treatingburners 84 which raise the temperature of the metal polymer laminate toat least the temperature of the lowest melting point of any polymer inthe molten film from either extruder slot die. An infrared temperaturesensor 85 measures the temperature to ensure the correct temperature isreached and controlled. Several temperature sensors can be used acrossthe width, or it may be automated and continuously moved side to sideacross the width to ensure quality control of the temperature to ensurean even temperature profile. An insulated holding box 86 holds thetemperature of the metal polymer laminate at the post treat temperaturefor a defined period based on the line speed and the length of the box,and then the elevated temperature metal polymer laminate is cooled withan air knife blower 87 to reduce the temperature to solidify the polymerof the metal polymer laminate. The target temperature of the metalpolymer laminate immediately following the air knife depends upon thenatural cooling zone 89 immediately following, the line speed, thetarget temperature at the idle rolls just before the winding reel, andprimarily the desired polymer properties on the metal substrate. Theamount of air out of the air knife, that is the air pressure in theknife, can be varied to obtain the desired temperature. The polymersolidification point can be delayed somewhat, if desired, and allowed tohappen in the cooling zone 89. The cooled laminate then travels aroundthe exit deflector rolls and is wound up on a winding reel.

The extruder dies in FIG. 8 are fed by extruders, heated piping, and acombination block where multiple extruder outputs are combined, such asdesired and suitable for laminating onto a metal substrate. A one, two,or three layer molten film structure is developed for hot laminatingonto the metal substrate in the most common applications. The niprollers 83 are water cooled, and controlled at an elevated temperaturesuch as allows the film to bond, without adhering to the nip rollers.The film structure preferably includes a tie layer, and the tie layer isoriented next to the steel.

Either one of the extruder slot dies 82 a,b may be omitted and a solidfilm roll used to provide a second coating. In this manner, the coatingis a combined solid film and a molten film coating. This may beeconomically advantageous in certain situations. For example, if a clearcoating and a colored coating is used, the clear coating (solid) wouldrequire a low film inventory and the color coating (molten) wouldrequire a low pellet inventory as it would only need to be made asrequired based on order fulfillment. The clear coating could bepurchased and the color coating could be adaptive based on a feedbackloop and compensate for metal substrate variances.

The extrusion coating is one method of economical production, butdepending upon commercial factors may not be the optimum cost. Orderschedule, cost of runs, the ability to run continuously, the amount ofscrap, and number of coils in an order for example, all become a part ofthe line economics. An extrusion line is generally very reliable, butquality issues in the film are expensive if it causes the metalsubstrate to be scrapped. Typical applications of film are approximately35 to 100 lbs of polymer per ton of metal substrate, depending uponmarkets, so the substrate cost is a highly significant component to lineoperation.

Example 1

A metal strip 0.009″ thick galvanized steel was run on a line configuredsimilar to FIG. 1 with the exception that an impinging flame was used asa post treat rather than an induction furnace. A 1.5 mil two layer filmwas applied comprising: a semi crystalline polyester PBT with a whitecolor, and a tie layer primarily composed of an anhydride-modifiedethylene acrylate tie layer. The ratio of the tie layer to the bulklayer was approximately 1:4. The Metal strip was preheated toapproximately 300° F. and post treated to between 510-520° F. afterlamination. The laminator rolls were heated to 400° F. and the linespeed was operated at 20 feet per minute. No forced air cooling wasapplied to the metal-polymer laminate. After post treating the metalstrip stayed molten for approximately 22 seconds, solidified, and thencooled for an additional 9 seconds before contacting the exit deflectorroll where the large roll acted as a heat sink and rapidly cooled themetal-laminate to ambient temperature. The metal strip exhibited all thedesired commercial properties of: adhesion over 43 ounces per inch basedon a cross hatch adhesion test (using a 3M 610 tape), bending toughnessat a one metal thickness without metal exposure, and a pencil hardnessof HB.

Example 2

A metal strip 0.010″ thick galvanized steel was run on a line configuredas in example 1. A 0.6 mil two layer film was applied to one side of themetal strip comprising: a semi crystalline polyester PBT without color,and a tie layer primarily composed of an anhydride-modified ethyleneacrylate tie layer. The ratio of the tie layer to the bulk layer wasapproximately 3:17. The Metal strip was preheated to approximately 300°F. and post treated to between 440-450° F. after lamination. Thelaminator rolls were heated to 400° F. and the line speed was operatedat 12 feet per minute. No forced air cooling was applied to themetal-polymer laminate. The metal strip exhibited all the desiredcommercial properties of: adhesion over 43 ounces per inch based on across hatch adhesion test (using a 3M 610 tape), bending toughness at aone metal thickness without metal exposure, and a pencil hardness of 2B.Over 500 feet of continuous steel was run coated 18″ wide with polymerin a continuous length with a surface free of defects that would becompletely acceptable in the marketplace.

Example 3

A metal strip 0.010″ thick galvanized steel was run on a line configuredas in example 1. Two films were applied to the metal strip. A 0.6 miltwo layer film was applied to one side of the metal strip comprising: asemi crystalline polyester PBT without color, and a tie layer primarilycomposed of an anhydride-modified ethylene acrylate tie layer. The ratioof the tie layer to the bulk layer was approximately 3:17. The otherside received a 0.6 mil two layer film comprising: a highly crystallinepolyester PBT with a white color utilizing TiO2, and a tie layerprimarily composed of an anhydride-modified ethylene acrylate tie layer.The ratio of the tie layer to the bulk layer was approximately 3:17. TheMetal strip was preheated to approximately 300° F. and post treated tobetween 440-450° F. after lamination. The laminator rolls were heated to400° F. and the line speed was operated at 15 feet per minute. Themetal-polymer laminate was allowed to air cool. The metal stripexhibited all the desired commercial properties of: adhesion over 43ounces per inch based on a cross hatch adhesion test (using a 3M 610tape), bending toughness at a zero metal thickness without metalexposure, and a pencil hardness of 2B for the clear and HB for the whitecolor. Over 500 feet of continuous steel was run coated 18″ wide withpolymer in a continuous length with a surface free of defects that wouldbe completely acceptable in the marketplace. The line could clearly havebeen operated for a longer period, but operation was chosen to bestopped as a steady state operation was clearly achieved.

Example 4

A metal strip 0.010″ thick galvanized steel was run on a line configuredas in and post treated per example 3. Two films were applied to themetal strip in a similar arrangement and operation as example 3. An 0.8mil was applied to each side with a white color similar to the whitecolor film of example 3. The metal strip exhibited all the desiredcommercial properties of: adhesion over 43 ounces per inch based on across hatch adhesion test (using a 3M 610 tape), bending toughness at azero metal thickness without metal exposure, and a pencil hardness ofHB. Over 500 feet of continuous steel was run coated 18″ wide withpolymer in a continuous length with a surface free of defects that wouldbe completely acceptable in the marketplace.

Example 5

A metal strip 0.010″ thick galvanized steel was run on a line configuredas in and post treated per example 3. Two films were applied to themetal strip in a similar arrangement with the only difference being thethickness and color of the films. An 0.8 mil PBT was applied to one sideand a 0.6 mil PBT was applied to the other. The metal strip exhibitedall the desired commercial properties of: adhesion over 43 ounces perinch based on a cross hatch adhesion test (using a 3M 610 tape), bendingtoughness at a zero metal thickness without metal exposure, and a pencilhardness of HB. Over 500 feet of continuous steel was run coated 18″wide with polymer in a continuous length with a surface free of defectsthat would be completely acceptable in the marketplace.

Example 6

Two different metal strips were run on the line configured as follows:strip 1 was a 0.010″ thick G30 galvanized steel strip 18″ wide and strip2 was a 0.015″ thick G30 galvanized steel strip 24″ wide. The linespeeds for both strips were 12 to 25 feet per minute. The preheattemperature range of the metal strips were between 305° F. to 350° F.The post heat temperature range was observed between 420° F. to 440° F.

Example 6 continued. For Strip 1, a 0.6 mil PBT clear film was appliedto one side and a 1.0 mil PBT white color was applied to the other side.The white color film was split into five film widths with gaps of 1/16,½″, 1, and 2″. Strip 2 was similarly coated to its full width.

Example 6 continued. The pencil hardness for strip 1 was 2B on the clearcolor, and strip 1 passed the zero T bending test with 100% continuityand passed the cross hatch adhesion test (using a 3M 610 tape). Thepencil hardness for strip 2 was HB to H on the white color, and strip 2passed the zero T bending test with 100% continuity and passed the crosshatch adhesion test (using a 3M 610 tape).

Example 7

Gloss reduction. A surface sandpaper of 400 grit finish wassimultaneously applied to both sides of a small sample of polymer todemonstrate the ability of the polymer to lower the gloss by alteringthe surface finish of the polymer. For the samples, a 0.6 mil two layertie layer/PBT clear film was applied to one side and a two layer 1.5 miltie layer/PBT white color was applied to the other side. Two polymersamples were prepared by melting them above the melting point of thePBT. While still in the melted state, the samples were passed through anip roller with the sandpaper where the grit finish was impressed uponthe polymer surface to a near perfect replication. The polymer coatedsamples also immediately cooled below the melting point of the film inthe nip roller and did not adhere to the sandpaper. A gloss (60 degree)measurement of the polymer surface obtained readings of 6-8 gloss units.Prior to the alteration of the surface finish, the gloss readings were35-40 gloss units.

Example 8

Gloss control comparison. A cooling roll with a surface finish averagingapproximately 8 micro inches was used to develop a white film forlaminating which was applied to the surface of a galvanized metalsubstrate as described in example 1 with the exception that a post treattemperature was utilized well below the melting point of the PBT, atapproximately 200° F. The surface finish of the film was thereforesubstantially unaltered through laminating and post treating. Thepolymer coated strip was allowed to cool by convection naturally on theprocessing line and coiled. Gloss (60 degree) measurements of the whitecolor polymer surface obtained readings of 60-65 gloss units.

Example 9

High hardness with bending capability and chemical corrosion capability.A long continuous sample of a laminated metal (over 1,000 feet) was madeusing a 1.5 mil polyester film, with a 85% semi crystalline PBT bulklayer over a 15% PETG tie layer, onto both sides of a smooth galvanizedmetal substrate, that was simultaneously preheated and pretreated to atemperature of 250-300° F., then simultaneously laminated on both sideswithout visible entrapped air, then post treated to 475-525° F., heldabove the melting point of the PBT for approximately 30 seconds asmeasured by an infrared thermometer, then air cooled gently to thesolidification point, then cooled to approximately 120-150° F. over aninterval of 30 seconds on a line running at 20-25 fpm. The metal thenpassed over deflector rolls and wound up at substantially ambienttemperature. On a sample basis, the laminate had properties of 5H pencilhardness and passed cross hatch adhesion tests. The coating also passedzero T bend tests without splitting, and was able to withstand boiltesting in a flat panel at 250° F. in a pressurized container of 3% saltwater by weight without visible corrosion or blistering on the substrateunder the flat panel area. The coating also was able to pass a crosshatch adhesion test after the boil test.

Example 10

Similar to example 9, a tin free steel sample using the same two layercoating 0.8 mils thick, was processed in the same manner except that thecooling after post heat was performed using an air knife to rapidlyforce the coating to solidify immediately after being held at 475-525°F. for 30 seconds, and then allowed to air cool and wound up atessentially ambient temperature. The pencil test was 2H and the coatingpassed cross hatch adhesion coatings, boil testing, and zero T bendingas in example 9. The coating was subsequently successfully formed into adraw-redraw 9 inch tall can suitable for an aerosol application.

All of the above examples were run without any visible air entrapmentbetween the metal substrate and the film. Air entrapment was not visibleeven when viewed under magnification capable of seeing bubbles as smallas 0.5 micron in diameter.

While various embodiments of the present invention have been described,the invention may be modified and adapted to various operational methodsto those skilled in the art. Therefore, this invention is not limited tothe description and figure shown herein, and includes all suchembodiments, changes, and modifications that are encompassed by thescope of the claims.

We claim:
 1. Processing steps for laminating a metal substrate with athin thermoplastic polymer film to create desirable simultaneouscommercial properties comprising: a. uncoiling a metal substrate from acoil on a processing line, b. wherein said metal substrate is flatrolled, c. increasing the surface energy of a first major side of saidmetal substrate to a dyne/cm level of at least 45, d. preheating saidmetal substrate to at least 200° F., e. preselecting a first film forbonding to said first major side, wherein said first film is eithersolid or molten, f. pressing said first film onto said first major sideby use of a first roll, g. utilizing a first chemical bond for adheringsaid first film to said first major side thereby creating a metalpolymer laminate, h. wherein said first film comprises at least 50%thermoplastic polyester by weight, i. wherein said polyester is PET,PBT, or a mixture of PET and PBT, j. wherein said first film is amaximum of 0.003 inches thick, k. wherein said first film comprises atleast one layer, l. post treating said metal polymer laminate by heatingsaid metal polymer laminate to at least the lowest melting point of anypolymer in said first film, and m. cooling said metal polymer laminateto below 150° F. for coiling into a finished coil, n. wherein saidcooling of said metal polymer laminate creates crystallinity in saidfirst film according to a predetermined criterion, and whereby saidfinished coil has said desirable simultaneous commercial propertiescomprising: o. coating continuity of at least three metal thicknessbending radius without metal exposure, p. bonding of said first filmonto said metal substrate of at least 43 ounces per inch after saidcooling, q. a minimum pencil hardness of 2B.
 2. The processing stepsaccording to claim 1 wherein the following steps are optionally doneprior to said post treating of said metal polymer laminate: r.additionally heating said metal polymer laminate to at least 200° F. ifnecessary, s. increasing the surface energy of the second major side ofsaid metal substrate to a dyne/cm level of at least 45, t. preselectinga second film for bonding to the second major side of said metalsubstrate, r. pressing said second film onto the second major side byuse of a second roll, wherein said second film is either solid ormolten, u. wherein said second roll is i. opposite of said first roll tocreate a roll nip, or ii. a selected distance sequentially after saidfirst roll, v. utilizing a second chemical bond for adhering said secondfilm to the second major side, w. wherein said second film comprises atleast one layer, and x. wherein said second film is a maximum of 0.003inches thick.
 3. The processing steps according to claim 2 wherein anysaid film is trimmed to substantially match the width of said metalsubstrate prior to being pressed against said metal substrate.
 4. Theprocessing steps according to claim 2 wherein the crystallinity of anysaid polyester is maximized by timing said cooling of polymer metallaminate.
 5. The processing steps according to claim 2 wherein any saidchemical bond is created by use of an anhydride, acrylic acid, glycol,or an acrylate molecular group.
 6. The processing steps according toclaim 2 wherein at least one of the group comprising i) said first rolland ii) said second roll is heated to a controlled temperature.
 7. Theprocessing steps according to claim 2 wherein said processing lineincludes strip storage to allow coils to be spliced together inline. 8.The processing steps according to claim 2 wherein any said preheating orpost heating is automatically regulated based on the lengthwise speed ofsaid metal substrate on said processing line and includes any efficiencyeffects that vary with the lengthwise speed of said metal substrate onsaid processing line.
 9. The processing steps according to claim 2wherein said chemical bond is created by use of a PETG tie layer, andsaid cooling provides a pencil hardness of a minimum of 5H.